It is well known that an optical waveguide is a physical structure which guides electromagnetic waves (e.g. light) through the structure. The guidance, or confinement, of light by the waveguide is the result of internal reflections within the waveguide. As a physical event, these internal reflections result when the difference between the refractive index, nwg, of the waveguide material, and that of the surrounding environment, ne, has a certain value. Otherwise, there may be no confinement, or inefficient confinement, of light within the waveguide.
It is also well known that an applied electric field can change the refractive index of a material through a linear or nonlinear electro-optic effect such as the well-known Pockels' effect (linear) or the Kerr effect (nonlinear). In particular, the Pockels' electro-optic effect is a case wherein the influence of a voltage that is applied across a material will change the index of refraction, n, of the material by an amount, Δn, which can be mathematically expressed as:Δn=−rn3E/2where r is the Pockels' constant, and E is the strength of the electric field. In the context of a planar, waveguide coupler switch, an electric field E is applied between two cross-coupled optical waveguides which are separated by an electro-optic material having a refractive index, neo. When applied, the electric field, E, changes the refractive index, neo, of the cross-coupling material to modify the cross-coupling characteristics between the two optical waveguides. As a result, light traveling along one waveguide is moved to the other waveguide.
With the above in mind, the design of a vertical, waveguide optical switch as envisioned for the present invention involves several interactive factors of particular importance. These include: the separation distance, d, between the waveguides (i.e. the thickness of the cross-coupling material); the refractive index of the cross-coupling material, nc, (also sometimes referred to herein as neo); and the design (i.e. configuration) of the electric field E.
In particular, insofar as the design of the electric field is concerned, the ability of the device (i.e. electro-optic switch) to configure and confine the electric field, E, relative to the cross-coupling material is of paramount importance. Specifically, the concern here for a design of the electric field, E, is three-fold. First: the electric field, E, passing through the cross-coupling material should be uniform (i.e. the electric field flux lines are parallel to each other). Second: flux lines of the electric field, E, should be confined to the cross-coupling material. And third: the flux lines of the electric field, E, should be aligned with the polarization direction of the cross-coupling material (i.e. perpendicular to the light beam pathway in the waveguides). The purpose for harmonizing these factors is to optimize the electro-optic modulation efficiency of the device.
In light of the above, it is an object of the present invention to provide an electro-optically coupled switch having a cross-coupling material with a refractive index, nc, that ensures good optical confinement between two waveguides. Another object of the present invention is to provide an electro-optically coupled switch with a cross-coupling material having a refractive index, nc, that establishes a strong electro-optic modulation coefficient. Yet another object of the present invention is to design the structure for an electro-optic switch having the proper waveguide separation to achieve strong waveguide cross-coupling; while maximizing the electro-optic efficiency of the device by providing good optical confinement in the cross-coupling material that facilitates the transfer of light into or out of the waveguide. Another object of the present invention is to provide an electro-optically coupled switch wherein a uniform electric field, E, is confined and directed through a layer of cross-coupling material that is sandwiched between two optical waveguides, and wherein the electric field intensity is normal to the layer of cross-coupling material. Still another object of the present invention is to provide an electro-optically coupled switch that is simple to manufacture, is easy to use and is comparatively cost effective.